I've always been skeptical of happiness statistics. In many cases, self-reporting happiness offers an objective floor for happiness, but the ceiling is entirely relative/subjective.

The floor is universal: starvation, suffering, death.

The ceiling...

For someone who's starving & facing death, would simply be good health, easy access to food, healthy family, house & car.

But the ceiling for someone who already has these things is different. The ceiling for a billionaire is different.

The only way I can imagine not doing this type of subjective self-reporting is... maybe you can draw blood from populations and record cortisol and oxytocin levels?